This competing grant renewal proposes continued study of the pathologic human inner ear following the basic strategy of the previous grant period, that is the use of light and electron microscopy. We plan a sharply focused area of investigation, namely cochlear neuronal degeneration in the human cochlear implant patient and its impact on speech recognition. We now have collected temporal bones from 16 individuals who were implanted during life. In nine of these, the auditory brainstem is also available. Initially we will plan to studythe implanted cochleas and morphometric parameters of thecochlear nucleus on both the stimulated and nonstimulated sides and to correlate these parameters with individual performance during life using the cochlear implant. Since the most dramatic central change might be expected in the neuropil of the cochlear nucleus, we also propose synaptophysin immunostaining to evaluate the density of synapses in the cochlear nucleus on stimulated and nonstimulated sides. This investigation can be expected to better predict remaining neuronal elements in human patients who are candidates for cochlear implantation and perhaps to explain the variability in speech recognition scores of these patients.